The present invention relates to an optical pumping laser with a resonator.
Referring to FIG. 1, there is shown a typical optical pumping laser system comprising an apertured input mirror 3 and an output mirror 4 spaced apart from the input mirror 3. A pumping beam 1 is produced from a pumping laser (not shown). In this arrangement, the pumping beam 1 and an oscillation laser beam 2 exist coaxially with each other. The laser system shown in FIG. 1 is of guite simplified construction, but its drawbacks are as follows: First, (i) since the pumping beam 1 is focused and injected into the system through an aperture provided in the input mirror 3, it is difficult to provide a uniform excitation of a laser medium having a large cross-section, with the result that the excitation efficiency of the laser and the mode quality are degraded. Further, (ii) since the output mirror 4 not only functions as means for outputting the oscillation laser beam 2 but also functions as a reflection mirror for the pumping beam 1, care must be taken especially with respect to the output mirror 4. Even if such a measure is taken, laser loss or loss of pumping beam is not avoidable. In addition, (iii) when the output mirror 4 is moved for frequency tuning, the condition of the pumping beam returning from the output mirror 4 to the pumping laser varies, thus providing disturbance in the pumping beam, resulting in degraded stability of the entire laser system.
To overcome these drawbacks, a resonator configured as shown in FIG. 2 has been proposed and put into practice (For instance IEEE. J. of Q.E, 1980, QE-16, p 505). In this laser resonator, a Brewster plate 5 and a reflection mirror 6 are used instead of the input mirror 3, and an output mirror 4 is used, wherein a laser amplification region LA is formed between the Brewster plate 5 and the output mirror 4. However, this system utilizes only a surface reflection on the Brewster plate 5 to constitute the laser resonator, with the result that laser loss is large and only pulse oscillation having a high gain is possible. In other words, with this system, a continuous oscillation having a low gain cannot be realized. Further, because of the large optical loss of this Brewster plate 5 for the oscillation laser beam, the oscillation laser beam is outputted from the output mirror 4, which is located far from the Brewster plate 5. Then, the output mirror 4 is hit by the pumping beam 1. So, the system shown in FIG. 2 cannot still overcome the drawbacks, described in the above items (ii) and (iii), of the first-mentioned system. This is a serious problem particularly in the continuous oscillation.